Co-existence of the Onodi cell with the variation of perisphenoidal structures

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European Archives of Oto-Rhino-Laryngologyand Head & Neck ISSN 0937-4477 Eur Arch OtorhinolaryngolDOI 10.1007/s00405-012-2325-8

Co-existence of the Onodi cell with thevariation of perisphenoidal structures

Orhan Ozturan, Alper Yenigun, NazanDegirmenci, Fadlullah Aksoy & BayramVeyseller

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RHINOLOGY

Co-existence of the Onodi cell with the variationof perisphenoidal structures

Orhan Ozturan • Alper Yenigun • Nazan Degirmenci •

Fadlullah Aksoy • Bayram Veyseller

Received: 30 August 2012 / Accepted: 11 December 2012

� Springer-Verlag Berlin Heidelberg 2012

Abstract The presence of the Onodi cell (OC) may be

accompanied by morphological variations of the neigh-

boring anatomic structures. Such variations carry signifi-

cant surgical implications and challenges. Pneumatization

of the sphenoid sinus induces anterior clinoid pneumati-

zation (ACP), affects the type of the Vidian nerve (VN)

canal or alters the courses of the internal carotid artery

(ICA), and the optic nerves (ONs) are strongly depending

on it. Onodi cell pneumatization may reach and surround

the optic nerve in various extension. Our aim in the study

was to investigate the effect of Onodi cell’s potential

co-existence on these structures. This study was planned as

a retrospective and cross-sectional study. This study per-

formed in a tertiary referral center. Coronal computerized

tomography images of 999 patients were examined. Using

an 64 slices tomography machine, images taken at 3-mm

sections were reconstructed using a bone algorithm and

evaluated. OCs were present at 212 of the total 320 sides in

160 patients. Type-2 was found to be the most prevalent

type of VN canal configuration (Type-2: VN canal partially

protrudes into the sphenoid sinus or into the floor of the

sphenoid) among all patients (66.5 %) and among those

with OCs (71.2 %). The presence or absence of the OC did

not cause a statistically significant alteration of the int-

rasphenoidal course of the VN. The presence of OCs was

found to be significant (p \ 0.01) in accompanying pneu-

matization of the anterior clinoid process (34.4 %, 73/212),

protrusion (80.1 %, 170/212) and dehiscence (36.3 %,

77/212) of the optic nerve, and protrusion (59 %, 125/212)

and dehiscence (20.8 %, 44/212) of the ICA. In 108/320

sides where OCs were absent, no significant correlations

existed. This study shows that in the co-existence of an OC,

ACP, protrusion and dehiscence of the optic nerve and ICA

are encountered at significantly higher rates, while the

course of the VN is not necessarily altered.

Keywords Onodi cell � Vidian nerve � Optic nerve �Anterior clinoid process � Internal carotid artery �Paranasal sinuses � Computer tomography

Introduction

The Onodi cell (OC), also called the sphenoethmoidal cell,

is an ethmoidal air cell located at the most posterior end of

the ethmoid bone which pneumatizes into the sphenoid

sinus. It was first described in the 1900s by Adolf Onodi

(1857–1920), and was named after him [1]. Most authors

report the incidence of the OC as 8–14 % [2]. Due to its

intimate relationship with the optic nerve (ON) and the

internal carotid artery (ICA), assessing its presence before

surgery will help reduce the potential risk of injury to those

structures [3].

The Vidian nerve (VN) canal runs along the anterior

border of the foramen lacerum, over the floor of the

sphenoid sinus, extending into the pterygopalatine fossa.

VN enters the pterygopalatine fossa and joins the spheno-

palatine ganglion at its posterior side [4]. The protrusion or

dehiscence of VN canal may render VN vulnerable in

endoscopic manipulations of the sphenoid sinus area, and

in sinus diseases [5]. According to CT findings, VN con-

figuration is classified into three types [6]. Those three

O. Ozturan � N. Degirmenci � F. Aksoy � B. Veyseller

Department of Otorhinolaryngology, Bezmialem Vakif

University, Istanbul, Turkey

A. Yenigun (&)

Karaman State Hospital, Otorhinolaryngology Clinic,

Turgut Ozal Street No:1, Karaman, Turkey

e-mail: [email protected]

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Eur Arch Otorhinolaryngol

DOI 10.1007/s00405-012-2325-8

Author's personal copy

types, as defined by Lee et al. are Type-1: VN canal

completely protrudes into the sphenoid sinus (Fig. 1),

Type-2: VN canal partially protrudes into the sphenoid

sinus or into the floor of the sphenoid (Fig. 2), and Type-3:

VN canal is completely embedded in the sphenoid corpus

(Fig. 3). Computerized tomography (CT) is considered as

the best tool for visualizing paranasal sinuses [7]. Before

any endoscopic operation to sphenoid sinus, important

structures adjacent to this sinus should be detected by CT

investigation.

A study authored by Simmen et al. [8] showed that the

existence of pneumatized supraorbital ethmoid cells sig-

nificantly altered the course of the anterior ethmoidal

artery. This finding may as well be paralleled by the

co-existence of the OC, may alter the morphological

changes in the floor and/or the lateral wall of the sphenoid

sinus. Pneumatization of the sphenoid sinus induces ACP,

affects the type of the VN canal or alters the courses of the

ICA and the optic nerves are strongly depending on it.

Onodi cell pneumatization may reach and surround the

optic nerve in various extension. Our study was aimed to

investigate the effect of Onodi cell’s potential co-existence

on these structures.

Methods

This is a retrospective study, approved by the local Clinical

Research Ethics Committee, evaluating coronal paranasal

sinus CT (Philips Brilliance 64-slice CT scanner, Philips

Medical Imaging, The Netherlands) images. The images

were taken at 3-mm sections and reconstructed using a

bone algorithm and evaluated. CT images were taken in

three planes (coronal, axial, sagittal). Coronal images

perpendicular to hard plate were investigated. The

vomerine crest was accepted as midline. Vidian canal was

demonstrated with CT imaging and its localization and

bony structures were studied. The relationships of the

Vidian canal to the sphenoid sinus, including whether it

was embedded in the bone, protruded into the bone, or was

linked to bone lamella in the sinus were examined.

All CT images were ordered for sinonasal, otologic and

maxillofacial injuiries, between January and June 2011.

Fig. 1 Coronal CT image showing protrusion of bilateral ON

(arrowhead), bilateral ACP (point star), protrusion of Vidian canal

(type-1) (triangle), pneumatization of bilateral PP (square) associated

with protrusion and dehiscence of left maxillary nerve (circle)

Fig. 2 Coronal CT image showing protrusion and dehiscence of

right ON (arrowhead), pneumatization of right PP (square), Vidian

canal type-2 (triangle) and right OC

Fig. 3 Coronal CT image showing protrusion of bilateral ON

(arrowhead), Vidian canal type-3 (triangle) and right OC


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Patients with nasal poliposis or sinus anomalies, and those

who had previous sinus surgery were excluded from the

study. In the evaluation of coronal sinus CTs, the perpen-

dicular lamina and the hard palate were preferably posi-

toned in right angles. OCs and the courses of VN canals

were noted in a total of 1,998 sphenoid sinuses in 999

patients. The presence of Onodi cell was determined fol-

lowing Stammberger et al. in that the optic nerve bulging

into a posterior ethmoid cell qualifies for an Onodi cell.

The radiological criteria for definition of the OC was to be

a posterior etmoid cell that invaded the superior portion of

the sphenoid to partially surround the optic canal.

According to CT findings, VN configuration is classified

into three types using classification introduced by Lee et al.

Those three types are Type-1: VN canal completely pro-

trudes into the sphenoid sinus, Type-2: VN canal partially

protrudes into the sphenoid sinus or into the floor of the

sphenoid, and Type-3: VN canal is completely embedded

in the sphenoid corpus. Evaluations of CT scans were

carried out by two otolaringologists and all of the films

read by two of them. The sections where the OC was seen

obviously were taken for evaluation. VN canals, ACPs,

ICAs and ONs were meticulously examined in CTs

showing unilateral and bilateral OCs. Configuration types

of the VN canal, and protrusion and dehiscence of ICA and

ON were classified according to the above mentioned cri-

teria. The categorical data were evaluated by the Chi

square analyses. Differences at the level of p \ 0.05 were

accepted to be statistically significant.

Results

The 999 patients examined by coronal paranasal sinus CTs

consisted of 537 males and 462 women, with an age range

of 13–91 years and a mean age of 36.4 years. Onehundred-

sixty of the 999 patients had the OC. The incidence of OC

is 16.6 %. Those 160 patients consisted of 93 males and 67

women, with an age range of 13–91, and a mean age of

40.8.

In a total of 160 patients, 66.3 % sides had the OC (212/

320 sides). 32.5 % of the patients had bilateral OCs,

36.3 % had OCs on the right side, and 31.3 % had OCs on

the left. The heights of the OC images seen in the coronal

section CTs were measured. The mean height was found to

be 0.84 cm (minimum 0.3 cm and maximum 1.6 cm).

The presence of the OC was 11 % on the right side,

10.2 % on the left side, with a total of 10.6 % on both

sides. The anatomical variations of the 999 patients (1998

VN canals) were evaluated according to the method

described above. The prevalence of Type-1 was 7 % on the

right side, 7.8 % on the left, with a total prevalence of

7.4 % on both sides. Type-2 had a prevalence of 65.1 % on

the right, 67.8 % on the left, and 66.5 % when both sides

were taken together. Type-3 had a prevalence of 27.8 % on

the right, 24.3 % on the left, and 26 % on both sides.

The types of VN canal, ACP, protrusion and dehiscence

of ICA and of ON were examined of the 160 patients (320

sides). At the right side, the configuration of VN canal was

Type-2 in 66.4 % of the patients with OCs, 84 % in

patients without the OC. At the left, Vidian canal Type-2

was seen in 76.5 % of the patients with OCs, 63.8 % in

patients without the OC. The correlation of the presence of

the OC with the type of VN canal configuration was

evaluated by the Chi square test. No statistically significant

correlation was found (p = 0.67 on the right, p = 0.19 on

the left) (Table 1).

The types of VN canal configurations were also exam-

ined in the overall patient population, and Type-2 was

found to be the most common type (66.5 %). The most

prevalent type of VN canal in patients with OCs was also

found to be Type-2 (71.2 %) (Fig. 4). The presence of the

OC and the type of VN canal did not have a significant

statistical correlation (p = 0.92 on the right side, p = 0.83

on the left). Statistically, the presence of the OC did not

significantly alter the intrasphenoidal course of VN.

On the right, 32.7 % of the patients with an OC had

ACP; that rate was 4 % in patients without an OC

(p \ 0.01). On the left, 36.3 % of the patients with an

OC had ACP; the rate was 5.2 % in those without an OC

(p \ 0.01). The overall co-existence of the OC and ACP

was found to be 34.4 %, while the presence of ACP

without the presence of an OC was 4.6 %. The co-exis-

tence of ACP and the OC had a significant correlation on

both sides (p \ 0.01) (Table 2).

On the right side, the co-existence of ON protrusion and

the OC was found to be 76.4 %, while ON protrusion was

24 % in patients without an OC (p \ 0.01). On the left

side, the co-existence of ON protrusion and the OC was

found to be 84.3 %, while ON protrusion was only 7 % in

patients without an OC (p \ 0.01). The overall rate of the

co-existence of ON protrusion and the OC was 80.1 %, and

the presence of ON protrusion in the absence of an OC was

17.6 %. The co-existence of ON protrusion and the OC was

found to be statistically significant on both sides (p \ 0.01)

(Table 1).

On the right, the co-existence of ON dehiscence and the

OC was 30.9 %, while the prevalence of ON dehiscence

was 0 % in those patients without an OC (p \ 0.01). On

the left, the co-existence of ON dehiscence and the OC was

42.2 %, while the prevalence of ON dehiscence was 0 % in

those patients without an OC (p \ 0.01).

The total occurence of ON dehiscence in the presence of

the OC was 36.3, and 0 % (0/108) in the absence of an OC.

The co-existence of ON dehiscence with the OC was sta-

tistically significant on both sides (p \ 0.01) (Table 1).


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On the right side, the co-existence of ICA protrusion and

the OC was seen in 59.1 % of the patients, while only 6 %

of those without an OC had ICA protrusion (p \ 0.01). On

the left, the co-existence of ICA protrusion and the OC was

seen in 58.8 %, while the rate of ICA protrusion was 5.2 %

in those without an OC (p \ 0.01). The overall prevalence

of ICA protrusion was found to be 59 % in the presence of

the OC, and 5.6 % without the OC (p \ 0.01). The corre-

lation between ICA protrusion and the presence of the OC

was found to be statistically significant on both sides

(Table 1).

On the right side, the co-existence of ICA dehiscence

and the OC was present in 19.1 % of the patients, while

ICA dehiscence was present in 6 % of those without an OC

(p \ 0.01). On the right side, the co-existence of ICA

dehiscence and the OC was present in 21.8 % of the

patients, while no ICA dehiscence was seen in those

without an OC: 0 % (p \ 0.01). The overall rate of prev-

alence of ICA dehiscence was found to be 20.8 % in the

presence of the OC, and 5.6 % without a coexisting OC

(p \ 0.01). The correlation between ICA dehiscence and

the presence of the OC was found to be statistically sig-

nificant on both sides (Table 1).

Discussion

Sphenoid sinus is one of the most difficult sinuses in par-

anasal sinuses for surgery and is surrounded with important

structures. These structures include ON, ICA, VN, and they

Table 1 Vidian nerve canal

types in different conditionsAll patients Right Left Total

VN canal type 1 7.0 % (70/999) 7.8 % (78/999) 7.4 % (148/1998)

VN canal type 2 65.1 % (651/999) 67.8 % (678/999) 66.5 % (1329/1998)

VN canal type 3 27.8 % (278/999) 24.3 % (243/999) 26.0 % (521/1998)

In the presence of the OC

VN canal type 1 6.4 % (7/110) 3.9 % (4/102) 5.1 % (11/212)

VN canal type 2 66.4 % (73/110) 79.5 % (78/102) 71.2 % (151/212)

VN canal type 3 27.3 % (30/110) 19.6 % (20/102) 23.5 % (50/212)

Fig. 4 Typing the Vidian nerve canal in subject with and without

OC population

Table 2 ACP protrusion and

dehiscence of the OC and ICA

ACP anterior clinoid

pneumatization, ICA internal

carotid artery, OC Onodi cell,

ON optic nerve, PP pterygoid

process, VN Vidian nerve

Right Left Total

In the presence of the OC

PACP 32.7 % (36/110) 36.3 % (37/102) 34.4 % (73/212)

ON protrusion 76.4 % (84/110) 84.3 % (86/102) 80.1 % (170/212)

ON dehiscence 30.9 % (34/110) 42.2 % (43/102) 36.3 % (77/212)

ICA protrusion 59.1 % (65/110) 58.8 % (60/102) 58.9 % (125/212)

ICA dehiscence 19.1 % (21/110) 21.8 % (23/102) 20.8 % (44/212)

In the abscence of the OC

PACP 4 % (2/50) 5.2 % (3/58) 4.6 % (5/108)

ON protrusion 24 % (12/50) 7 % (7/58) 17.6 % (19/108)

ON dehiscence 0 % (0/50) 0 % (0/58) 0 % (0/108)

ICA protrusion 6 % (3/50) 5.2 % (3/58) 5.6 % (6/108)

ICA dehiscence 6 % (3/50) 0 % (0/58) 2.8 % (3/108)


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are separated from sphenoid sinus by very thin bony lam-

elle. Dehiscence would occur on these bone lamelles

occasionally and the risk of damage on these structures gets

higher during any operation to this site. Before any endo-

scopic operation on this site, variations of these important

structures should be detected by CT investigation.

Most authors report the incidence of the OC as 8–14 %

[2]. In our study we found 9.42 % compatible with the

relevant literature.

The relationship of ON with the posterior paranasal

sinus is classified in terms of protrusion and dehiscence

(Figs. 1, 2, 3, 5) [9, 10]. When more than a half ([50 %) of

the nerve protruded into the sinus cavity as seen in coronal

CT sections, protrusion was confirmed. Dehiscence of the

bone was acknowledged when no bone density separating

ON from the sinus was present in CT images.

In another study conducted in 1996 with 150 patients

classifies ON in four types according to its relationship

with posterior paranasal sinuses [11].

Type-1: ON runs a course adjacent to the sphenoid

sinus, but makes no indentation on the wall of the sinus,

Type-2: ON runs a course adjacent to the sphenoid

sinus, and makes some indentation on the wall,

Type-3: ON runs a course through the sphenoid sinus,

Type-4: ON runs a course adjacent to the sphenoid sinus

and posterior ethmoidal cells.

Injuries of the ON are encountered as complications of

sinus diseases and also accompanying surgical traumas,

especially in the presence of protrusion and dehiscence. If

the nerve is surgically injured while still inside the sinus,

the risk of blindness is considerably high [12]. Infections of

the sphenoid sinus or a mucocele compressing the optic

canal or the ON may also lead to visual impairment.

Compression of the ON may lead to ischemia of the nerve

or to venous congestion. It is reported that development

of an OC may be accompanied by protrusion of the ON

[9, 10]. Studies conducted in the years of 2000, 2006, 2008

and 2009 reported significant correlations between protru-

sion of the ON inside the sphenoid sinus and ACP [9, 10,

13, 14].

ICA runs a critical course inside the sphenoid sinus,

located posterolaterally [9]. ICA can also be protruded or

dehiscent (Figs. 6, 7). If the surgeon is not aware of these

variations preoperatively, fatal complications may be

encountered. Controlling an intrasphenoidal ICA bleeding

is quite difficult. Even if the bleeding is successfully con-

trolled, irreversible neurologic sequels may entail [9]. In a

study involving 92 patients, Sirikci et al. [9] reported a

26.1 % prevalence of ICA protrusion and a 22.8 % prev-

alence of ICA dehiscence. Fuji et al. [15] noted that among

the 25 cadavers in their series, 8 % had ICA dehiscence in

the sphenoid sinus. Kennedy et al. [16] found that the rate

of ICA dehissence in sphenoid sinuses was 20–25 %. In

our study, ICA protrusion and dehissence were found as

2.8 % in the absence of an OC; when the OC was present,

these rates increased to 59 % for protrusion, and to 20.8 %

for dehissence of the ICA. Thus, with the presence of the

OC, ICA protrusion and dehissence rates increased very

significantly. Another finding in our study showed that

increased height of the OC correlated significantly with

higher rates of protrusion and dehissence of the ICA.

The configuration of the VN canal as seen in CT images

was classified by Lee et al. in three types, according to the

relationship of VN with the floor of the sphenoid sinus

[16]. Lang and Keller reported that 38 % of their 150 cases

exhibited VN canal configuration Type-3, 34 % had Type-

2, and 18 % had Type-1 [17]. Yazar et al. [18] again in a

series of 150 cases reported a 54 % prevalence of Type-2,

36 % of Type-1, and 10 % of Type-3 using a different

definition of VN canal classification; they also noted a

32 % dehiscence rate of the bony structure. Liu et al. [19]

examined 341 patients, where they also classified VN

canal, using Lee et al.’s definition, in three types according

to its relationship with the floor of the sphenoid, and

reported a 53.4 % prevalence of Type-3 (embedded in the

sphenoid corpus), 34.2 % of Type-2, and 12.5 % of Type-1

in their series. In our study, we noted that VN canal Type-2

was the most prevalent type (66.5 %) among our 999

patients, followed by Type-3 (26 %) and Type-1 (7.4 %).

With a coexistent OC, the course of VN canal was found to

be Type-2 in a great majority (71.2 %) of the patients. The

presence of an OC did not significantly alter the intrasph-

enoidal course of VN; also the height of the OC did not

cause a significant alteration on the course of VN canal.


bilateral ON (arrowhead), bilateral ACP (point star), pneumatization

of bilateral PP (square) and bilateral OC


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The results of our study showed significant correlations

between the presence of the OC and ACP 34.4 %, ON

protrusion 80.1 % and dehissence 36.3 %, and ICA pro-

trusion 59 % and dehissence 20.8 % (p \ 0.01). When the

OC was absent, those rates were much lower: 4.6 % for

ACP, 17.6 % for protrusion and 0 % for dehissence of the

ON, and 5.6 % for protrusion and 2.8 % for dehissence of

the ICA.

When the above study is adapted for classifying pro-

trusion of ON, Type-1 and Type-2 stand for \50 % pro-

trusion, and Types 3 and 4 stand for [50 % protrusion of

ON; Type-1 was found to be the most common type, with a

rate of 76 % [12]. Another study dating from 2004

evaluated ON in 100 patients, using the same classification,

and again Type-1 was the most common type, with a rate

of 64 % [11]. In our study, in the absence of an OC[50 %

protrusion of ON had a rate of 17.6 % (19/108) which was

compatible with the relevant literature [20]. When the OC

was present, [50 % protrusion rate of ON increased to

80.1 % (170/212), which showed a statistically significant

correlation between the presence of an OC and protrusion

of ON (p \ 0.01).

Eventhough pneumatization of bilateral pterygoid pro-

cess has not been observed in the past studies, it was

observed in three patients in our study (Figs. 1, 4, 5).

Conclusion

The results of this study demonstrated that the presence of

the OC did not cause a significant alteration in the int-

rasphenoidal course of VN, but its presence caused a sig-

nificant increase in ACP, and in protrusion and dehissence

of both ON and of the ICA. Increased height of the OC

correlated significantly with higher rates of protrusion and

dehissence of the ICA and ACP, on the contrary this sig-

nificance did not replicate for the course of VN canal and

protrusion and dehissence of the ON.

These observations point out the importance of careful

preoperative CT analyses in preparation for surgery of the

sphenoid sinus area, and of delineating a specific roadmap

for each patient. Preoperative discovery of the prevalance

of OC is an indispensible necessity in ensuring the safety of

sphenoid sinus surgery.

Acknowledgments The authors would like to thank to Ass. Prof.

Omer Uysal, PhD, from the Department of Biostatistics and Medical

informatics for his kind statistical assistance.

Conflict of interest None.

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Fig. 7 Coronal CT image showing protrusion and dehiscence of left

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OC


bilateral ICAs (white arrow), protrusion of bilateral ON (arrow)

bilateral ACP (point star), pneumatization of bilateral PP (square)

and bilateral OC


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Co-existence of the Onodi cell with the variation of perisphenoidal structures

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